1. Field of the Invention
The present invention relates to an axial gear drive train and method for driving the gear drive train. More particularly, the invention relates to a gear drive train and method for actuating the gear drive train particularly adapted for use with a heliostat to correct the daily position thereof such that the heliostat follows seasonal solar declination changes.
2. Description of the Prior Art
A heliostat is a device known in the prior art. A heliostat, through the use of an automated reflector, tracks the passage of the sun in a manner so as to provide a stationary reflected beam output from the tracking reflector. As with all celestial tracking equipment, the heliostat must be oriented in azimuth and in elevation. The azimuth line of orientation is a true north-south meridian. The elevation angle is the polar angle defining the local elevation angle between Earth and the celestial pole. Once established, azimuthal axis and the polar axis remain as fixed references for the heliostat device. The position of the sun, however, is a variable which must be tracked with reasonable accuracy if a stationary reflected beam output of the heliostat is to result.
The operation of the heliostat must take into account both the twenty-four hour cyclic nature of the apparent movement of the sun across the Earth's sky as the Earth rotates as well as solar declination. Thus, to track the sun's daily rotation, the heliostat must be rotated about its polar axis one revolution per twenty-four hour day. Driving mechanisms are available for rotating the heliostat about its axis so as to track the sun as the Earth rotates. One such driving mechanism is described in my co-pending application, Ser. No. 205,769, filed Nov. 10, 1980, entitled Step Motor Drive System for Heliostat.
Solar declination is the angular deviation from perpendicularity of the sun's rays with respect to the polar axis. If the sun's rays strike the polar axis at an angle of ninety (90) degrees, the solar declination is said to be zero degrees. This is the situation at the Spring Equinox.
As the sun moves in the Ecliptic, it moves higher in the sky. Its rays, intersecting the polar axis, appear to be leaning toward the northern pole until at Summer Solstice, the solar declination is said to be about 23.5.degree. north. Having achieved its height at the peak of summer, following the Ecliptic, the sun descends in the sky until it crosses the celestial equator once again thereby achieving zero degree solar declination: Autumnal Equinox.
The elevation angle of the sun in the sky continues to decrease until it reaches its furthermost declination at the Winter Solstice at which its rays intersect the polar axis again at an angle of 23.5.degree. south. This solar declination is repeated annually as the sun defines the Ecliptic as it moves from south to north and back to south each year.
As aforesaid, the heliostat must take into account both variations of the apparent movement of the sun with respect to the Earth: the twenty-four hour and the annual solar declination cyclic periods. The heliostat, in itself, would appear to be a simple device. A mirror is positioned so that the sun's rays striking its surface are reflected at an angle parallel to the polar axis. A drive mechanism, such as described in my aforementioned co-pending application, is provided to rotate the mirror as the sun apparently travels westwardly across the sky. The mirror must also be tilted about an axis perpendicular to the polar axis to adjust to the solar declination. As is true with the twenty-four hour cyclic period of the sun's movement, the solar rate of declination is not uniform. Thus, ordinary clock work mechanisms are not adequate to provide accurate tracking of the heliostat with the sun's movement.
The basic heliostat, in and of itself, is relatively inexpensive. However, the methods for adjusting movement of the heliostat to accurately track the sun can be cost prohibitive, if not a nuisance, to prevent commercial use of the heliostat. For instance, to track solar declination, both manual and electrical schemes have been used utilizing slip rings feeding a servo-mechanism from an angle computer remotely located.
Thus, a need exists for a simple, inexpensive driving mechanism for tilting the mirror surface of the heliostat to accurately track the solar declination.
Accordingly, it is an object of the present invention to provide a parasitically driven axial gear drive mechanism.
Another object of the present invention is to provide a parasitically driven gear train mechanism for tilting the mirror and mirror assembly of a heliostat wherein the heliostat tracks the solar declination.
Still another object of the present invention is to provide an improved and relatively inexpensive declinator for a heliostat to be utilized in the tracking operation of the heliostat.